Inductively coupled RF plasma reactor and plasma chamber enclosure structure therefor

ABSTRACT

A plasma chamber enclosure structure for use in an RF plasma reactor. The plasma chamber enclosure structure being a single-wall dielectric enclosure structure of an inverted cup-shape configuration and having ceiling with an interior surface of substantially flat conical configuration extending to a centrally located gas inlet. The plasma chamber enclosure structure having a sidewall with a lower cylindrical portion generally transverse to a pedestal when positioned over a reactor base, and a transitional portion between the lower cylindrical portion and the ceiling. The transitional portion extends inwardly from the lower cylindrical portion and includes a radius of curvature. The structure being adapted to cover the base to comprise the RF plasma reactor and to define a plasma-processing volume over the pedestal. The structure being formed of a dielectric material of silicon, silicon carbide, quartz, and/or alumina being capable of transmitting inductive power therethrough from an adjacent antenna.

RELATED APPLICATIONS

This application is a divisional of Ser. No. 09/675,319 filed Sep. 29,2000 by Kenneth S. Collins et al., herein incorporated by reference nowU.S. Pat. No. 6,444,085, which is a divisional of Ser. No. 08/648,254filed on May 13, 1996 by Kenneth S. Collins et al., herein incorporatedby reference now U.S. Pat. No. 6,165,311, which is acontinuation-in-part of Ser. No. 08/580,026 filed Dec. 20, 1995 byKenneth S. Collins et al. pending which is a continuation of Ser. No.08/041,796 filed Apr. 1, 1993 by Kenneth S. Collins et al. now U.S. Pat.No. 5,556,501 issued Sep. 17, 1996, which is a continuation of Ser. No.07/722,340 filed Jun. 27, 1991 now abandoned; and said Ser. No.08/648,254 is a continuation-in-part of Ser. No. 08/503,467 filed Jul.18, 1995 by Michael Rice et al. now U.S. Pat. No. 5,770,029 which is adivisional of Ser. No. 08/138,060 filed Oct. 15, 1993, U.S. Pat. No.5,477,975 issued Dec. 26, 1995; and said Ser. No. 08/648,254 is acontinuation-in-part of Ser. No. 08/597,577 filed Feb. 2, 1996 byKenneth Collins, issued as U.S. Pat. No. 6,077,384 on Jun. 20, 2000,which is a continuation-in-part of Ser. No. 08/521,668 filed Aug. 31,1995 (now abandoned), which is a continuation-in-part of Ser. No.08/289,336 filed Aug. 11, 1994 now abandoned, which is a continuation ofSer. No. 07/984,045 filed Dec. 1, 1992 (now abandoned), the disclosuresof which are incorporated herein by reference. In addition U.S.application Ser. No. 08/648,256 filed May 13, 1996 by Kenneth S. Collinset al. entitled “Plasma Reactor With Heated Source of aPolymer-Hardening Precursor Material” now U.S. Pat. No. 6,036,877discloses related subject matter.

BACKGROUND OF THE INVENTION

1. Technical Field

The invention is related to inductively coupled RF plasma reactors ofthe type having a reactor chamber ceiling overlying a workpiece beingprocessed and an inductive coil antenna adjacent the ceiling.

2. Background Art

Inductively coupled RF plasma reactors are employed to perform a varietyof processes on workpieces such as semiconductor wafers. Referring toFIG. 1, one type of inductively coupled RF plasma reactor has a reactorchamber 10 including a ceiling 12 and a cylindrical side wall 14. Apedestal 16 supports the workpiece 18, such as a semiconductor wafer, sothat the workpiece generally lies in a workpiece support plane, and abias RF power generator is coupled to the pedestal 16. A generallyplanar coil antenna 20 overlies the ceiling 12 and is coupled to aplasma source RF power generator 22. A chief advantage of inductivelycoupled RF plasma reactors over other types such as capacitively coupledones, is that a higher ion density can be achieved with the inductivelycoupled type.

Adequate etch selectivity is achieved by operating at higher chamberpressure. (The term etch selectivity refers to the ratio of etch ratesof two different materials exposed to etching in the reactor.) This isbecause the polymerization processes typically employed in a highdensity plasma etch reactor to protect underlying non-oxygen-containing(e.g., silicon, polysilicon or photoresist) layers during etching of anoverlying oxygen-containing (e.g., silicon dioxide) layer are moreefficient at higher chamber pressures (e.g., above about 20-500 mT) thanat lower pressures. Polymer precursor gases (e.g., fluorocarbon orfluorohydrocarbon gases) in the chamber tend to polymerize strongly onnon-oxygen-containing surfaces (such as silicon or photoresist),particularly at higher chamber pressures, and only weakly onoxygen-containing surfaces (such as silicon dioxide), so that thenon-oxygen-containing surfaces are relatively well-protected frometching while oxygen-containing surfaces (such as silicon dioxide) arerelatively unprotected and are etched. Such a polymerization processenhances the oxide-to-silicon etch selectivity better at higher chamberpressures because the polymerization rate is higher at higher pressuressuch as 100 mT. Therefore, it is desireable to operate at a relativelyhigh chamber pressure when plasma-etching oxygen-containing layers overnon-oxygen-containing layers. For example, under certain operatingconditions such as a chamber pressure of 5 mT, an oxide-to-photoresistetch selectivity of less than 3:1 was obtained, and raising the pressureto the 50-100 mT range increased the selectivity to over 6:1. Theoxide-to-polysilicon etch selectivity exhibited a similar behavior.

The problem with increasing the chamber pressure (in order to increaseetch selectivity) is that plasma ion spatial density distribution acrossthe wafer surface becomes less uniform. There are two reasons thisoccurs: (1) the electron mean free path in the plasma decreases withpressure; and (2) the inductive field skin depth in the plasma increaseswith pressure. How these two factors affect plasma ion spatial densitydistribution will now be explained.

With regard to item 1 above, the electron-to-neutral species elasticcollision mean free path length, which is inversely proportional tochamber pressure, determines the extent to which electrons can avoidrecombination with other gas particles and diffuse through the plasma toproduce a more uniform electron and ion distribution in the chamber.Typically, electrons are not generated uniformly throughout the chamber(due, for example, to a non-uniform inductive antenna pattern) andelectron diffusion through the plasma compensates for this and providesgreater electron and plasma ion spatial density distribution uniformity.(Electron spatial density distribution across the wafer surface directlyaffects plasma ion spatial density distribution because plasma ions areproduced by collisions of process gas particles with energeticelectrons.) Increasing chamber pressure suppresses electron diffusion inthe plasma, thereby reducing (degrading) plasma ion spatial densitydistribution uniformity.

This problem may be understood by reference to FIG. 1, in which theinductive antenna 20, due to its circular symmetry, has an antennapattern (i.e., a spatial distribution of the magnitude of the inducedelectric field) with a null or local minimum along the antenna axis ofsymmetry so that very few if any electrons are produced over the wafercenter. At low chamber pressures, electron diffusion into the space(“gap”) between the antenna 20 and the workpiece 18 is sufficient totransport electrons into the region near the wafer center despite thelack of electron production in that region, thereby providing a moreuniform plasma distribution at the wafer surface. With increasingpressure, electron diffusion decreases and so plasma ion distributionbecomes less uniform.

A related problem is that the overall plasma density is greater near theceiling 12 (where the density of hot electrons is greatest) than at theworkpiece 18, and falls off more rapidly away from the ceiling 12 aschamber pressure is increased. For example, the electron mean free pathin an argon plasma with a mean electron temperature of 5 eV at a chamberpressure of 1 mT is on the order of 10 cm, at 10 mT it is 1.0 cm and at100 mT it is 0.1 cm. Thus in a typical application, for a 5 cmceiling-to-workpiece gap, most of the electrons generated near theceiling 12 reach the workpiece at a chamber pressure of 1 mT (for amaximum ion density at the workpiece), and a significant number at 10mT, while at 100 mT few do (for a minimal ion density at the workpiece).Accordingly, it may be said that a high pressure regime is one in whichthe mean free path length is about {fraction (1/10)} or more of theceiling-to-workpiece gap. One way of increasing the overall plasma iondensity at the workpiece 18 (in order to increase etch rate and reactorthroughput) without decreasing the chamber pressure is to narrow the gapso that the mean free path length becomes a greater fraction of the gap.However, this exacerbates other problems created by increasing chamberpressure, as will be described further below.

With regard to item (2) above, the inductive field skin depthcorresponds to the depth through the plasma—measured downward from theceiling 12—within which the inductive field of the antenna 20 is nearlycompletely absorbed. FIG. 2 illustrates how skin depth in an argonplasma increases with chamber pressure above a threshold pressure ofabout 0.003 mT (below which the skin depth is virtually constant overpressure). FIG. 2 also illustrates in the dashed-line curve howelectron-to-neutral elastic collision mean free path length decreaseslinearly with increasing pressure. The skin depth function graphed inFIG. 2 assumes a source frequency of 2 MHz and an argon plasma densityof 5□10¹⁷ electrons/m³. (It should be noted that the correspondingplasma density for an electro-negative gas is less, so that the curve ofFIG. 2 would be shifted upward with the introduction of anelectro-negative gas.) The graph of FIG. 2 was derived using a collisioncross-section for an electron temperature of 5 eV in argon. (It shouldbe noted that with a molecular gas such as C₂F₆ instead of argon, thecollision cross-section is greater so that the skin depth is greater ata given pressure and the entire curve of FIG. 2 is shifted upward.) Ifthe chamber pressure is such that the inductive field is absorbed withina small fraction—e.g., {fraction (1/10)}th—of the ceiling-to-workpiecegap adjacent the ceiling 12 (corresponding to a pressure of 1 mT for a 5cm gap in the example of FIG. 2), then electron diffusion—throughout theremaining {fraction (9/10)}ths of the gap—produces a more uniform plasmaion distribution at the workpiece surface. However, as pressureincreases and skin depth increases—e.g., beyond about {fraction(1/10)}th of the gap, then electron diffusion tends to have less effect.Thus, a measure of a high skin depth regime is that in which the skindepth is at about {fraction (1/10)} or more of the source-to-workpiecegap length. For example, if the pressure is so great that skin depthequals the ceiling-to-workpiece spacing (corresponding to a pressure ofabout 100 mT for a 5 cm gap in the example of FIG. 2), then any antennapattern null or local minimum extends to the surface of the workpiece18, effectively preventing electron diffusion from compensating for theeffects of the antenna pattern null on the processing of the workpiece.Such problems can arise, for example, when the ceiling-to-workpiecespacing is decreased in order to increase overall plasma density at theworkpiece surface. A related problem with a small ceiling-to-workpiecespacing and a high chamber pressure is that electrons are lost not onlyto recombination with particles in the processing gas but are also lostto recombination by collisions with the surface of the ceiling 12 andthe workpiece 18, so that it is even more difficult for electronsgenerated in other regions to diffuse into the region adjacent theworkpiece center.

In summary, plasma ion density at the wafer can be enhanced by reducingthe gap between the axially symmetrical antenna/ceiling 20, 12 and theworkpiece 18. But if the gap is reduced so much that the inductive fieldskin depth becomes a substantial fraction (≧10%) of the gap, then iondensity at the workpiece center falls off significantly relative to theedge due to the antenna pattern's center null. However, for a smallerfraction of skin depth over gap and sufficient electron diffusion(characteristic of a low chamber pressure), electrons produced far fromthe workpiece center may diffuse into the center region before beinglost to gas phase recombination or surface recombination, therebycompensating for the antenna pattern's center null. But as the gap isreduced (to increase overall plasma density at the workpiece) andchamber pressure is increased (to enhance etch selectivity), then: (1)the induced electric field over the workpiece center approaches a nullso that no electrons are produced in that region, and (2) electronsproduced in other regions generally cannot diffuse to the workpiececenter region due to recombination with gas particles and chamber (e.g.,ceiling) surfaces.

Thus, as the wafer-to-coil distance is decreased by the reactor designer(in order to enhance plasma density near the wafer surface, forexample), the plasma ion density decreases at the wafer center andultimately, at very short wafer-to-antenna distances, becomes a centernull giving rise to an unacceptable process non-uniformity. For example,in a plasma etch process carried out in such a reactor, the etch rate atthe wafer center may be so much less than elsewhere that it becomesimpossible to perform a complete etch across the entire wafer surfacewithout over-etching near the wafer periphery. Conversely, it becomesimpossible to avoid over-etching at the wafer periphery withoutunder-etching the wafer center. Thus, the problem is to find a way todecrease the wafer-to-antenna distance without incurring a concomitantpenalty in process non-uniformity.

One approach for solving or at least ameliorating this problem isdisclosed in U.S. application Ser. No. 08/507,726 filed Jul. 26, 1995 byKenneth S. Collins et al. and entitled “Plasma Source with anElectronically Variable Density Profile”, which discloses that an outergenerally planar coil antenna 24 coupled to a second independentlycontrolled plasma source RF power generator 26 can be provided over theceiling 12 concentric with the inner coil antenna 20 of FIG. 1. Theefficacy of this solution can be seen from the graphs of FIGS. 3Athrough 3E. FIG. 3A illustrates the plasma ion density as a function ofradius from the center of the workpiece 18 for a workpiece-to-ceilingheight of 4 inches (10 cm), the curve labelled A being the ion densityproduced by the outer coil antenna 24 and the curve labelled B being theion density produced by the inner coil antenna 20. The total resultingplasma ion density is the sum of these two curves but is not depicted inthe drawing for the sake of simplicity. FIG. 3A shows that at a heightof 4 inches (10 cm), the outer coil antenna 24 produces a uniform plasmaion density distribution, the inner coil antenna 20 not being required.FIG. 3B corresponds to FIG. 3A for a reduced workpiece-to-ceiling heightof 3 inches (7.5 cm), and shows that a dip in plasma ion densityproduced by the outer coil antenna 24 is compensated by thecenter-dominated ion density produced by the inner coil antenna 20. FIG.3C corresponds to FIG. 3A for a further reduced workpiece-to-ceilingheight of 2.5 inches (6.25 cm), and shows that the compensation by theinner coil 20 for the center dip in the plasma ion density produced bythe outer coil 24 remains fairly effective as the workpiece-to-ceilingheight is further reduced, although a slight dip in the total resultingplasma ion density near the center would begin to appear below thisheight. As shown in FIG. 3D, a further reduction in workpiece-to-ceilingheight to only 1.25 inches (about 3.2 cm) yields a pronounced dip in theplasma ion densities produced by both the inner and outer coil antennas20, 24, so that there is very little compensation and the resultingplasma ion density (the sum of the two curves shown) is highlynon-uniform. As shown in FIG. 3E, the problem worsens as the height isfurther reduced to 0.8 inches (2 cm).

What FIGS. 3A-3E show is that even the use of inner and outer coilantennas to solve the problem of the null in plasma ion density near theworkpiece center may lose effectiveness as the workpiece-to-ceilingheight is reduced below certain values. Thus, the wafer-to-ceilingheight cannot be reduced below a factor of the skin depth withoutsacrificing process uniformity. On the other hand, unless thewafer-to-ceiling height can be so reduced, plasma density and processperformance is limited. Accordingly, there is a need for a way to reducethe workpiece-to-ceiling height without sacrificing process uniformity.

SUMMARY

A plasma chamber enclosure structure for use in an RF plasma reactorwhich includes a pedestal adapted to support a workpiece to beprocessed, a reactor base housing the pedestal, and a coil antennaadjacent the reactor and which is adapted to inductively couple RF powerinto the reactor. The plasma chamber enclosure structure being asingle-wall dielectric enclosure structure of an inverted cup-shapeconfiguration. The plasma chamber enclosure structure having a ceilingwith an interior surface of substantially flat conical configurationextending to a centrally located gas inlet such that when positionedover the base said interior surface is more distant from the pedestalover a center of the pedestal and closer to the pedestal over aperiphery of the pedestal.

The plasma chamber enclosure having a sidewall with a lower cylindricalportion generally transverse to the pedestal when positioned over thebase and a transitional portion between the lower cylindrical portionand the ceiling. The transitional portion extends inwardly from thelower cylindrical portion and includes a radius of curvature.

The plasma chamber enclosure structure being adapted to cover thereactor base to define a plasma-processing volume over the pedestal andcomprise the RF plasma reactor. The plasma chamber enclosure structurebeing capable of transmitting inductive power therethrough from anadjacent antenna. The plasma chamber enclosure structure being formed ofa dielectric material of silicon, silicon carbide, quartz, and/oralumina.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cut-away side view of an inductively coupled plasma reactorof the type employed in a co-pending U.S. patent application referred toabove employing generally planar coil antennas.

FIG. 2 is a log-log scale graph of induction field skin depth in aplasma in cm (solid line) and of electron-to-neutral elastic collisionmean free path length (dashed line) as functions of pressure in torr(horizontal axis).

FIG. 3A is a graph of plasma ion density as a function of radialposition relative to the workpiece center in the reactor of FIG. 1 for aworkpiece-to-ceiling height of 4 inches, the curves labelled A and Bcorresponding to plasma ion densities produced by outer and inner coilantennas respectively.

FIG. 3B is a graph of plasma ion density as a function of radialposition relative to the workpiece center in the reactor of FIG. 1 for aworkpiece-to-ceiling height of 3 inches, the curves labelled A and Bcorresponding to plasma ion densities produced by outer and inner coilantennas respectively.

FIG. 3C is a graph of plasma ion density as a function of radialposition relative to the workpiece center in the reactor of FIG. 1 for aworkpiece-to-ceiling height of 2.5 inches, the curves labelled A and Bcorresponding to plasma ion densities produced by outer and inner coilantennas respectively.

FIG. 3D is a graph of plasma ion density as a function of radialposition relative to the workpiece center in the reactor of FIG. 1 for aworkpiece-to-ceiling height of 1.25 inches, the curves labelled A and Bcorresponding to plasma ion densities produced by outer and inner coilantennas respectively.

FIG. 3E is a graph of plasma ion density as a function of radialposition relative to the workpiece center in the reactor of FIG. 1 for aworkpiece-to-ceiling height of 0.8 inches, the curves labelled A and Bcorresponding to plasma ion densities produced by outer and inner coilantennas respectively.

FIG. 4A is a cut-away side view of a plasma reactor in accordance withan alternative embodiment of the invention employing a singlethree-dimensional center non-planar solenoid winding.

FIG. 4B is an enlarged view of a portion of the reactor of FIG. 4Aillustrating a preferred way of winding the solenoidal winding.

FIG. 4C is a cut-away side view of a plasma reactor corresponding toFIG. 4A but having a dome-shaped ceiling.

FIG. 4D is a cut-away side view of a plasma reactor corresponding toFIG. 4A but having a conical ceiling.

FIG. 4E is a cut-away side view of a plasma reactor corresponding toFIG. 4D but having a truncated conical ceiling.

FIG. 5 is a cut-away side view of a plasma reactor in accordance withthe preferred embodiment of the invention employing inner and outervertical solenoid windings.

FIG. 6 is a cut-away side view of a plasma reactor in accordance with asecond alternative embodiment of the invention corresponding to FIG. 5in which the outer winding is flat.

FIG. 7A is a cut-away side view of a plasma reactor in accordance with athird alternative embodiment of the invention corresponding to FIG. 4Ain which the center solenoid winding consists of plural uprightcylindrical windings.

FIG. 7B is a detailed view of a first implementation of the embodimentof FIG. 7A.

FIG. 7C is a detailed view of a second implementation of the embodimentof FIG. 7A.

FIG. 8 is a cut-away side view of a plasma reactor in accordance with afourth alternative embodiment of the invention corresponding to FIG. 5in which both the inner and outer windings consist of plural uprightcylindrical windings.

FIG. 9 is a cut-away side view of a plasma reactor in accordance with afifth alternative embodiment of the invention corresponding to FIG. 5 inwhich the inner winding consists of plural upright cylindrical windingsand the outer winding consists of a single upright cylindrical winding.

FIG. 10 is a cut-away side view of a plasma reactor in accordance with asixth alternative embodiment of the invention in which a single solenoidwinding is placed at an optimum radial position for maximum plasma iondensity uniformity.

FIG. 11 is a cut-away side view of a plasma reactor in accordance with aseventh alternative embodiment of the invention corresponding to FIG. 4Ain which the solenoid winding is an inverted conical shape.

FIG. 12 is a cut-away side view of a plasma reactor in accordance withan eighth alternative embodiment of the invention corresponding to FIG.4A in which the solenoid winding is an upright conical shape.

FIG. 13 is a cut-away side view of a plasma reactor in accordance with aninth alternative embodiment of the invention corresponding to FIG. 4Ain which the solenoid winding consists of an inner upright cylindricalportion and an outer flat portion.

FIG. 14 is a cut-away side view of a plasma reactor in accordance with atenth alternative embodiment of the invention corresponding to FIG. 10in which the solenoid winding includes both an inverted conical portionand a flat portion.

FIG. 15 is a cut-away side view of a plasma reactor in accordance withan eleventh alternative embodiment of the invention corresponding toFIG. 12 in which the solenoid winding includes both an upright conicalportion and a flat portion.

FIG. 16 illustrates another embodiment of the invention employing acombination of planar, conical and dome-shaped ceiling elements.

FIG. 17A illustrates an alternative embodiment of the inventionemploying a separately biased silicon side wall and ceiling andemploying electrical heaters.

FIG. 17B illustrates an alternative embodiment of the inventionemploying separately biased inner and outer silicon ceiling portions andemploying electrical heaters.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In a plasma reactor having a small antenna-to-workpiece gap, in order tominimize the decrease in plasma ion density near the center region ofthe workpiece corresponding to the inductive antenna pattern centernull, it is an object of the invention to increase the magnitude of theinduced electric field at the center region. The invention accomplishesthis by concentrating the turns of an inductive coil overlying theceiling near the axis of symmetry of the antenna and maximizing the rateof change (at the RF source frequency) of magnetic flux linkage betweenthe antenna and the plasma in that center region.

In accordance with the invention, a solenoidal coil around the symmetryaxis simultaneously concentrates its inductive coil turns near the axisand maximizes the rate of change of magnetic flux linkage between theantenna and the plasma in the center region adjacent the workpiece. Thisis because the number of turns is large and the coil radius is small, asrequired for strong flux linkage and close mutual coupling to the plasmain the center region. (In contrast, a conventional planar coil antennaspreads its inductive field over a wide radial area, pushing the radialpower distribution outward toward the periphery.) As understood in thisspecification, a solenoid-like antenna is one which has plural inductiveelements distributed in a non-planar manner relative to a plane of theworkpiece or workpiece support surface or overlying chamber ceiling, orspaced at different distances transversely to the workpiece supportplane (defined by a workpiece supporting pedestal within the chamber) orspaced at different distances transversely to an overlying chamberceiling. As understood in this specification, an inductive element is acurrent-carrying element mutually coupled with the plasma in the chamberand/or with other inductive elements of the antenna.

A preferred embodiment of the invention includes dual solenoidal coilantennas with one solenoid near the center and another one at an outerperipheral radius. The two solenoids may be driven at different RFfrequencies or at the same frequency, in which case they are preferablyphase-locked and more preferably phase-locked in such a manner thattheir fields constructively interact. The greatest practicaldisplacement between the inner and outer solenoid is preferred becauseit provides the most versatile control of etch rate at the workpiececenter relative to etch rate at the workpiece periphery. The skilledworker may readily vary RF power, chamber pressure andelectro-negativity of the process gas mixture (by choosing theappropriate ratio of molecular and inert gases) to obtain a wider rangeor process window in which to optimize (using the present invention) theradial uniformity of the etch rate across the workpiece. Maximum spacingbetween the separate inner and outer solenoids of the preferredembodiment provides the following advantages:

(1) maximum uniformity control and adjustment;

(2) maximum isolation between the inner and outer solenoids, preventinginterference of the field from one solenoid with that of the other; and

(3) maximum space on the ceiling (between the inner and outer solenoids)for temperature control elements to optimize ceiling temperaturecontrol.

FIG. 4A illustrates a single solenoid embodiment (not the preferredembodiment) of an inductively coupled RF plasma reactor having a shortworkpiece-to-ceiling gap, meaning that the skin depth of the inductionfield is on the order of the gap length. As understood in thisspecification, a skin depth which is on the order of the gap length isthat which is within a factor of ten of (i.e., between about one tenthand about ten times) the gap length.

FIG. 5 illustrates a dual solenoid embodiment of an inductively coupledRF plasma reactor, and is the preferred embodiment of the invention.Except for the dual solenoid feature, the reactor structure of theembodiments of FIGS. 4A and 5 is nearly the same, and will now bedescribed with reference to FIG. 4A. The reactor includes a cylindricalchamber 40 similar to that of FIG. 1, except that the reactor of FIG. 4Ahas a non-planar coil antenna 42 whose windings 44 are closelyconcentrated in non-planar fashion near the antenna symmetry axis 46.While in the illustrated embodiment the windings 44 are symmetrical andtheir symmetry axis 46 coincides with the center axis of the chamber,the invention may be carried out differently. For example, the windingsmay not be symmetrical and/or their axis of symmetry may not coincide.However, in the case of a symmetrical antenna, the antenna has aradiation pattern null near its symmetry axis 46 coinciding with thecenter of the chamber or the workpiece center. Close concentration ofthe windings 44 about the center axis 46 compensates for this null andis accomplished by vertically stacking the windings 44 in the manner ofa solenoid so that they are each a minimum distance from the chambercenter axis 46. This increases the product of current (I) and coil turns(N) near the chamber center axis 46 where the plasma ion density hasbeen the weakest for short workpiece-to-ceiling heights, as discussedabove with reference to FIGS. 3D and 3E. As a result, the RF powerapplied to the non-planar coil antenna 42 produces greater induction[d/dt][N·I] at the wafer center—at the antenna symmetry axis46—(relative to the peripheral regions) and therefore produces greaterplasma ion density in that region, so that the resulting plasma iondensity is more nearly uniform despite the small workpiece-to-ceilingheight. Thus, the invention provides a way for reducing the ceilingheight for enhanced plasma process performance without sacrificingprocess uniformity.

The drawing of FIG. 4B best shows a preferred implementation of thewindings employed in the embodiments of FIGS. 4A and 5. In order thatthe windings 44 be at least nearly parallel to the plane of theworkpiece 56, they preferably are not wound in the usual manner of ahelix but, instead, are preferably wound so that each individual turn isparallel to the (horizontal) plane of the workpiece 56 except at a stepor transition 44 a between turns (from one horizontal plane to thenext).

The cylindrical chamber 40 consists of a cylindrical side wall 50 and acircular ceiling 52 integrally formed with the side wall 50 so that theside wall 50 and ceiling 52 constitute a single piece of material, suchas silicon. However, the invention may be carried out with the side wall50 and ceiling 52 formed as separate pieces, as will be described laterin this specification. The circular ceiling 52 may be of any suitablecross-sectional shape such as planar (FIG. 4A), dome (FIG. 4C), conical(FIG. 4D), truncated conical (FIG. 4E), cylindrical or any combinationof such shapes or curve of rotation. Such a combination will bediscussed later in this specification. Generally, the vertical pitch ofthe solenoid 42 (i.e., its vertical height divided by its horizontalwidth) exceeds the vertical pitch of the ceiling 52, even for ceilingsdefining 3-dimensional surfaces such as dome, conical, truncated conicaland so forth. The purpose for this, at least in the preferredembodiment, is to concentrate the induction of the antenna near theantenna symmetry axis, as discussed previously in this specification. Asolenoid having a pitch exceeding that of the ceiling 52 is referred toherein as a non-conformal solenoid, meaning that, in general, its shapedoes not conform with the shape of the ceiling, and more specificallythat its vertical pitch exceeds the vertical pitch of the ceiling. A2-dimensional or flat ceiling has a vertical pitch of zero, while a3-dimensional ceiling has a non-zero vertical pitch.

A pedestal 54 at the bottom of the chamber 40 supports a planarworkpiece 56 in a workpiece support plane during processing. Theworkpiece 56 is typically a semiconductor wafer and the workpiecesupport plane is generally the plane of the wafer or workpiece 56. Thechamber 40 is evacuated by a pump (not shown in the drawing) through anannular passage 58 to a pumping annulus 60 surrounding the lower portionof the chamber 40. The interior of the pumping annulus may be lined witha replaceable metal liner 60 a. The annular passage 58 is defined by thebottom edge 50 a of the cylindrical side wall 50 and a planar ring 62surrounding the pedestal 54. Process gas is furnished into the chamber40 through any one or all of a variety of gas feeds. In order to controlprocess gas flow near the workpiece center, a center gas feed 64 a canextend downwardly through the center of the ceiling 52 toward the centerof the workpiece 56 (or the center of the workpiece support plane). Inorder to control gas flow near the workpiece periphery (or near theperiphery of the workpiece support plane), plural radial gas feeds 64 b,which can be controlled independently of the center gas feed 64 a,extend radially inwardly from the side wall 50 toward the workpieceperiphery (or toward the workpiece support plane periphery), or baseaxial gas feeds 64 c extend upwardly from near the pedestal 54 towardthe workpiece periphery, or ceiling axial gas feeds 64 d can extenddownwardly from the ceiling 52 toward the workpiece periphery. Etchrates at the workpiece center and periphery can be adjustedindependently relative to one another to achieve a more radially uniformetch rate distribution across the workpiece by controlling the processgas flow rates toward the workpiece center and periphery through,respectively, the center gas feed 64 a and any one of the outer gasfeeds 64 b-d. This feature of the invention can be carried out with thecenter gas feed 64 a and only one of the peripheral gas feeds 64 b-d.

The solenoidal coil antenna 42 is wound around a housing 66 surroundingthe center gas feed 64 a. A plasma source RF power supply 68 isconnected across the coil antenna 42 and a bias RF power supply 70 isconnected to the pedestal 54.

Confinement of the overhead coil antenna 42 to the center region of theceiling 52 leaves a large portion of the top surface of the ceiling 52unoccupied and therefore available for direct contact with temperaturecontrol apparatus including, for example, plural radiant heaters 72 suchas tungsten halogen lamps and a water-cooled cold plate 74 which may beformed of copper or aluminum for example, with coolant passages 74 aextending therethrough. Preferably the coolant passages 74 a contain acoolant of a known variety having a high thermal conductivity but a lowelectrical conductivity, to avoid electrically loading down the antennaor solenoid 42. The cold plate 74 provides constant cooling of theceiling 52 while the maximum power of the radiant heaters 72 is selectedso as to be able to overwhelm, if necessary, the cooling by the coldplate 74, facilitating responsive and stable temperature control of theceiling 52. The large ceiling area irradiated by the heaters 72 providesgreater uniformity and efficiency of temperature control. (It should benoted that radiant heating is not necessarily required in carrying outthe invention, and the skilled worker may choose to employ an electricheating element instead, as will be described later in thisspecification.) If the ceiling 52 is silicon, as disclosed in co-pendingU.S. application Ser. No. 08/597,577 filed Feb. 2, 1996 by Kenneth S.Collins et al., then there is a significant advantage to be gained bythus increasing the uniformity and efficiency of the temperature controlacross the ceiling. Specifically, where a polymer precursor and etchantprecursor process gas (e.g., a fluorocarbon gas) is employed and wherethe etchant (e.g., fluorine) must be scavenged, the rate of polymerdeposition across the entire ceiling 52 and/or the rate at which theceiling 52 furnishes a fluorine etchant scavenger material (silicon)into the plasma is better controlled by increasing the contact area ofthe ceiling 52 with the temperature control heater 72. The solenoidantenna 42 increases the available contact area on the ceiling 52because the solenoid windings 44 are concentrated at the center axis ofthe ceiling 52.

The increase in available area on the ceiling 52 for thermal contact isexploited in a preferred implementation by a highly thermally conductivetorus 75 (formed of a ceramic such as aluminum nitride, aluminum oxideor silicon nitride or of a non-ceramic like silicon either lightly dopedor undoped) whose bottom surface rests on the ceiling 52 and whose topsurface supports the cold plate 74. One feature of the torus 75 is thatit displaces the cold plate 74 well-above the top of the solenoid 42.This feature substantially mitigates or nearly eliminates the reductionin inductive coupling between the solenoid 42 and the plasma which wouldotherwise result from a close proximity of the conductive plane of thecold plate 74 to the solenoid 42. In order to prevent such a reductionin inductive coupling, it is preferable that the distance between thecold plate 74 and the top winding of the solenoid 42 be at least asubstantial fraction (e.g., one half) of the total height of thesolenoid 42. Plural axial holes 75 a extending through the torus 75 arespaced along two concentric circles and hold the plural radiant heatersor lamps 72 and permit them to directly irradiate the ceiling 52. Forgreatest lamp efficiency, the hole interior surface may be lined with areflective (e.g., aluminum) layer. The center gas feed 64 a of FIG. 4Amay be replaced by a radiant heater 72 (as shown in FIG. 5), dependingupon the particular reactor design and process conditions. The ceilingtemperature is sensed by a sensor such as a thermocouple 76 extendingthrough one of the holes 75 a not occupied by a lamp heater 72. For goodthermal contact, a highly thermally conductive elastomer 73 such assilicone rubber impregnated with boron nitride is placed between theceramic torus 75 and the copper cold plate 74 and between the ceramictorus 75 and the silicon ceiling 52.

As disclosed in the above-referenced co-pending application, the chamber40 may be an all-semiconductor chamber, in which case the ceiling 52 andthe side wall 50 are both a semiconductor material such as silicon. Asdescribed in the above-referenced co-pending application, controllingthe temperature of, and RF bias power applied to, either the ceiling 52or the wall 50 regulates the extent to which it furnishes fluorinescavenger precursor material (silicon) into the plasma or,alternatively, the extent to which it is coated with polymer. Thematerial of the ceiling 52 is not limited to silicon but may be, in thealternative, silicon carbide, silicon dioxide (quartz), silicon nitrideor a ceramic.

As described in the above-referenced co-pending application, the chamberwall or ceiling 50, 52 need not be used as the source of a fluorinescavenger material. Instead, a disposable silicon member can be placedinside the chamber 40 and maintained at a sufficiently high temperatureto prevent polymer condensation thereon and permit silicon material tobe removed therefrom into the plasma as fluorine scavenging material. Inthis case, the wall 50 and ceiling 52 need not necessarily be silicon,or if they are silicon they may be maintained at a temperature (and/orRF bias) near or below the polymer condensation temperature (and/or apolymer condensation RF bias threshold) so that they are coated withpolymer from the plasma so as to be protected from being consumed. Whilethe disposable silicon member may take any appropriate form, in theembodiment of FIG. 4A the disposable silicon member is an annular ring62 surrounding the pedestal 54. Preferably, the annular ring 62 is highpurity silicon and may be doped to alter its electrical or opticalproperties. In order to maintain the silicon ring 62 at a sufficienttemperature to ensure its favorable participation in the plasma process(e.g., its contribution of silicon material into the plasma for fluorinescavenging), plural radiant (e.g., tungsten halogen lamp) heaters 77arranged in a circle under the annular ring 62 heat the silicon ring 62through a quartz window 78. As described in the above-referencedco-pending application, the heaters 77 are controlled in accordance withthe measured temperature of the silicon ring 62 sensed by a temperaturesensor 79 which may be a remote sensor such as an optical pyrometer or afluoro-optical probe. The sensor 79 may extend partially into a verydeep hole 62 a in the ring 62, the deepness and narrowness of the holetending at least partially to mask temperature-dependent variations inthermal emissivity of the silicon ring 62, so that it behaves more likea gray-body radiator for more reliable temperature measurement.

As described in U.S. application Ser. No. 08/597,577 referred to above,an advantage of an all-semiconductor chamber is that the plasma is freeof contact with contaminant producing materials such as metal, forexample. For this purpose, plasma confinement magnets 80, 82 adjacentthe annular opening 58 prevent or reduce plasma flow into the pumpingannulus 60. To the extent any polymer precursor and/or active speciessucceeds in entering the pumping annulus 60, any resulting polymer orcontaminant deposits on the replaceable interior liner 60 a may beprevented from re-entering the plasma chamber 40 by maintaining theliner 60 a at a temperature significantly below the polymer condensationtemperature, for example, as disclosed in the referenced co-pendingapplication.

A wafer slit valve 84 through the exterior wall of the pumping annulus60 accommodates wafer ingress and egress. The annular opening 58 betweenthe chamber 40 and pumping annulus 60 is larger adjacent the wafer slitvalve 84 and smallest on the opposite side by virtue of a slant of thebottom edge 50 a of the cylindrical side wall 50 so as to make thechamber pressure distribution more symmetrical with a non-symmetricalpump port location.

Maximum inductance near the chamber center axis 46 is achieved by thevertically stacked solenoidal windings 44. In the embodiment of FIG. 4A,another winding 45 outside of the vertical stack of windings 44 but inthe horizontal plane of the bottom solenoidal winding 44 b may be added,provided the additional winding 45 is close to the bottom solenoidalwinding 44 b.

Referring specifically now to the preferred dual solenoid embodiment ofFIG. 5, a second outer vertical stack or solenoid 90 of windings 92 atan outer location (i.e, against the outer circumferential surface of thethermally conductive torus 75) is displaced by a radial distance □R fromthe inner vertical stack of solenoidal windings 44. Note that in FIG. 5confinement of the inner solenoidal antenna 42 to the center and theouter solenoidal antenna 90 to the periphery leaves a large portion ofthe top surface of the ceiling 52 available for direct contact with thetemperature control apparatus 72, 74, 75, as in FIG. 4A. An advantage isthat the larger surface area contact between the ceiling 52 and thetemperature control apparatus provides a more efficient and more uniformtemperature control of the ceiling 52.

For a reactor in which the side wall 50 and ceiling 52 are formed of asingle piece of silicon for example with an inside diameter of 12.6 in(32 cm), the wafer-to-ceiling gap is 3 in (7.5 cm), and the meandiameter of the inner solenoid was 3.75 in (9.3 cm) while the meandiameter of the outer solenoid was 11.75 in (29.3 cm) using {fraction(3/16)} in diameter hollow copper tubing covered with a 0.03 thickteflon insulation layer, each solenoid consisting of four turns andbeing 1 in (2.54 cm) high. The outer stack or solenoid 90 is energizedby a second independently controllable plasma source RF power supply 96.The purpose is to permit different user-selectable plasma source powerlevels to be applied at different radial locations relative to theworkpiece or wafer 56 to permit compensation for known processingnon-uniformities across the wafer surface, a significant advantage. Incombination with the independently controllable center gas feed 64 a andperipheral gas feeds 64 b-d, etch performance at the workpiece centermay be adjusted relative to etch performance at the edge by adjustingthe RF power applied to the inner solenoid 42 relative to that appliedto the outer solenoid 90 and adjusting the gas flow rate through thecenter gas feed 64 a relative to the flow rate through the outer gasfeeds 64 b-d. While the present invention solves or at least amelioratesthe problem of a center null or dip in the inductance field as describedabove, there may be other plasma processing non-uniformity problems, andthese can be compensated in the versatile embodiment of FIG. 5 byadjusting the relative RF power levels applied to the inner and outerantennas 42, 90. For effecting this purpose with greater convenience,the respective RF power supplies 68, 96 for the inner and outersolenoids 42, 90 may be replaced by a common power supply 97 a and apower splitter 97 b which permits the user to change the relativeapportionment of power between the inner and outer solenoids 42, 90while preserving a fixed phase relationship between the fields of theinner and outer solenoids 42, 90. This is particularly important wherethe two solenoids 42, 90 receive RF power at the same frequency.Otherwise, if the two independent power supplies 68, 96 are employed,then they may be powered at different RF frequencies, in which case itis preferable to install RF filters at the output of each RF powersupply 68, 96 to avoid off-frequency feedback from coupling between thetwo solenoids. In this case, the frequency difference should besufficient to time-average out coupling between the two solenoids and,furthermore, should exceed the rejection bandwidth of the RF filters.Another option is to make each frequency independently resonantlymatched to the respective solenoid, and each frequency may be varied tofollow changes in the plasma impedance (thereby maintaining resonance)in lieu of conventional impedance matching techniques. In other words,the RF frequency applied to the antenna is made to follow the resonantfrequency of the antenna as loaded by the impedance of the plasma in thechamber. In such implementations, the frequency ranges of the twosolenoids should be mutually exclusive. Preferably, however, the twosolenoids are driven at the same RF frequency and in this case it ispreferable that the phase relationship between the two be such as tocause constructive interaction or superposition of the fields of the twosolenoids. Generally, this requirement will be met by a zero phase anglebetween the signals applied to the two solenoids if they are both woundin the same sense. Otherwise, if they are oppositely wound, the phaseangle is preferably 180□. In any case, coupling between the inner andouter solenoids can be minimized or eliminated by having a relativelylarge space between the inner and outer solenoids 42, 90, as will bediscussed below in this specification.

The range attainable by such adjustments is increased by increasing theradius of the outer solenoid 90 to increase the spacing between theinner and outer solenoids 42, 90, so that the effects of the twosolenoids 42, 90 are more confined to the workpiece center and edge,respectively. This permits a greater range of control in superimposingthe effects of the two solenoids 42, 90. For example, the radius of theinner solenoid 42 should be no greater than about half the workpieceradius and preferably no more than about a third thereof. (The minimumradius of the inner solenoid 42 is affected in part by the diameter ofthe conductor forming the solenoid 42 and in part by the need to providea finite non-zero circumference for an arcuate—e.g., circular—currentpath to produce inductance.) The radius of the outer coil 90 should beat least equal to the workpiece radius and preferably 1.5 or more timesthe workpiece radius. With such a configuration, the respective centerand edge effects of the inner and outer solenoids 42, 90 are sopronounced that by increasing power to the inner solenoid the chamberpressure can be raised into the hundreds of mT while providing a uniformplasma, and by increasing power to the outer solenoid 90 the chamberpressure can be reduced to on the order of 0.01 mT while providing auniform plasma. Another advantage of such a large radius of the outersolenoid 90 is that it minimizes coupling between the inner and outersolenoids 42, 90.

FIG. 5 indicates in dashed line that a third solenoid 94 may be added asan option, which is desireable for a very large chamber diameter.

FIG. 6 illustrates a variation of the embodiment of FIG. 5 in which theouter solenoid 90 is replaced by a planar winding 100.

FIG. 7A illustrates a variation of the embodiment of FIG. 4A in whichthe center solenoidal winding includes not only the vertical stack 42 ofwindings 44 but in addition a second vertical stack 102 of windings 104closely adjacent to the first stack 42 so that the two stacks constitutea double-wound solenoid 106. Referring to FIG. 7B, the doubly woundsolenoid 106 may consist of two independently wound single solenoids 42,102, the inner solenoid 42 consisting of the windings 44 a, 44 b, and soforth and the outer solenoid 102 consisting of the winding 104 a, 104 band so forth. Alternatively, referring to FIG. 7C, the doubly woundsolenoid 106 may consist of vertically stacked pairs of at least nearlyco-planar windings. In the alternative of FIG. 7C, each pair of nearlyco-planar windings (e.g., the pair 44 a, 104 a or the pair 44 b, 104 b)may be formed by helically winding a single conductor. The term “doublywound” used herein refers to winding of the type shown in either FIG. 7Bor 7C. In addition, the solenoid winding may not be merely doubly woundbut may be triply wound or more and in general it can consists of pluralwindings at each plane along the axis of symmetry. Such multiple-woundsolenoids may be employed in either one or both the inner and outersolenoids 42, 90 of the dual-solenoid embodiment of FIG. 5.

FIG. 8 illustrates a variation of the embodiment of FIG. 7A in which anouter doubly wound solenoid 110 concentric with the inner doubly woundsolenoid 106 is placed at a radial distance δR from the inner solenoid106.

FIG. 9 illustrates a variation of the embodiment of FIG. 8 in which theouter doubly wound solenoid 110 is replaced by an ordinary outersolenoid 112 corresponding to the outer solenoid employed in theembodiment of FIG. 5.

FIG. 10 illustrates another preferred embodiment in which the solenoid42 of FIG. 5 is placed at a location displaced by a radial distance δRfrom the center gas feed housing 66. In the embodiment of FIG. 4A, δR iszero while in the embodiment of FIG. 10 δR is a significant fraction ofthe radius of the cylindrical side wall 50. Increasing δR to the extentillustrated in FIG. 10 may be helpful as an alternative to theembodiments of FIGS. 4A, 5, 7A and 8 for compensating fornon-uniformities in addition to the usual center dip in plasma iondensity described with reference to FIGS. 3D and 3E. Similarly, theembodiment of FIG. 10 may be helpful where placing the solenoid 42 atthe minimum distance from the chamber center axis 46 (as in FIG. 4)would so increase the plasma ion density near the center of the wafer 56as to over-correct for the usual dip in plasma ion density near thecenter and create yet another non-uniformity in the plasma processbehavior. In such a case, the embodiment of FIG. 10 is preferred whereδR is selected to be an optimum value which provides the greatestuniformity in plasma ion density. Ideally in this case, δR is selectedto avoid both under-correction and over-correction for the usual centerdip in plasma ion density. The determination of the optimum value for δRcan be carried out by the skilled worker by trial and error steps ofplacing the solenoid 42 at different radial locations and employingconventional techniques to determine the radial profile of the plasmaion density at each step.

FIG. 11 illustrates an embodiment in which the solenoid 42 has aninverted conical shape while FIG. 12 illustrates an embodiment in whichthe solenoid 42 has an upright conical shape.

FIG. 13 illustrates an embodiment in which the solenoid 42 is combinedwith a planar helical winding 120. The planar helical winding has theeffect of reducing the severity with which the solenoid winding 42concentrates the induction field near the center of the workpiece bydistributing some of the RF power somewhat away from the center. Thisfeature may be useful in cases where it is necessary to avoidovercorrecting for the usual center null. The extent of such diversionof the induction field away from the center corresponds to the radius ofthe planar helical winding 120. FIG. 14 illustrates a variation of theembodiment of FIG. 13 in which the solenoid 42 has an inverted conicalshape as in FIG. 11. FIG. 15 illustrates another variation of theembodiment of FIG. 13 in which the solenoid 42 has an upright conicalshape as in the embodiment of FIG. 12.

The RF potential on the ceiling 52 may be increased, for example toprevent polymer deposition thereon, by reducing its effective capacitiveelectrode area relative to other electrodes of the chamber (e.g., theworkpiece and the sidewalls). FIG. 16 illustrates how this can beaccomplished by supporting a smaller-area version of the ceiling 52′ onan outer annulus 200, from which the smaller-area ceiling 52′ isinsulated. The annulus 200 may be formed of the same material (e.g.,silicon) as the ceiling 52′ and may be of a truncated conical shape(indicated in dashed line) or a truncated dome shape (indicated in solidline). A separate RF power supply 205 may be connected to the annulus200 to permit more workpiece center versus edge process adjustments.

FIG. 17A illustrates a variation of the embodiment of FIG. 5 in whichthe ceiling 52 and side wall 50 are separate semiconductor (e.g.,silicon) pieces insulated from one another having separately controlledRF bias power levels applied to them from respective RF sources 210, 212to enhance control over the center etch rate and selectivity relative tothe edge. As set forth in greater detail in above-referenced U.S.application Ser. No. 08/597,577 filed Feb. 2, 1996 by Kenneth S. Collinset al., the ceiling 52 may be a semiconductor (e.g., silicon) materialdoped so that it will act as an electrode capacitively coupling the RFbias power applied to it into the chamber 40 and simultaneously as awindow through which RF power applied to the solenoid 42 may beinductively coupled into the chamber 40. The advantage of such awindow-electrode is that an RF potential may be established directlyover the wafer 56 (e.g., for controlling ion energy) while at the sametime inductively coupling RF power directly over the wafer 56. Thislatter feature, in combination with the separately controlled inner andouter solenoids 42, 90 and center and peripheral gas feeds 64 a, 64 b-dgreatly enhances the ability to adjust various plasma process parameterssuch as ion density, ion energy, etch rate and etch selectivity at theworkpiece center relative to the workpiece edge to achieve an optimumuniformity. In this combination, the respective gas flow rates throughindividual gas feeds are individually and separately controlled toachieve such optimum uniformity of plasma process parameters.

FIG. 17A illustrates how the lamp heaters 72 may be replaced by electricheating elements 72′. As in the embodiment of FIG. 4A, the disposablesilicon member is an annular ring 62 surrounding the pedestal 54.

FIG. 17B illustrates another variation in which the ceiling 52 itselfmay be divided into an inner disk 52 a and an outer annulus 52 belectrically insulated from one another and separately biased byindependent RF power sources 214, 216 which may be separate outputs of asingle differentially controlled RF power source.

In accordance with an alternative embodiment, a user-accessible centralcontroller 300 shown in FIGS. 17A and 17B, such as a programmableelectronic controller including, for example, a conventionalmicroprocessor and memory, is connected to simultaneously control gasflow rates through the central gas feed 64 a and the peripheral gasfeeds 64 b-d, RF plasma source power levels applied to the inner andouter antennas 42, 90 and RF bias power levels applied to the ceiling 52and side wall 50 respectively (in FIG. 17A) and the RF bias power levelsapplied to the inner and outer ceiling portions 52 a, 52 b (in FIG.17B), temperature of the ceiling 52 and the temperature of the siliconring 62. A ceiling temperature controller 218 governs the power appliedby a power source 220 to the heaters 72′ by comparing the temperaturemeasured by the ceiling temperature sensor 76 with a desired temperatureknown to the controller 300. A ring temperature controller 222 controlsthe power applied by a heater power source 224 to the heater lamps 77facing the silicon ring 62 by comparing the ring temperature measured bythe ring sensor 79 with a desired ring temperature stored known to thecontroller 222. The master controller 300 governs the desiredtemperatures of the temperature controllers 218 and 222, the RF powerlevels of the solenoid power sources 68, 96, the RF power levels of thebias power sources 210, 212 (FIG. 17A) or 214, 216 (FIG. 17B), the waferbias level applied by the RF power source 70 and the gas flow ratessupplied by the various gas supplies (or separate valves) to the gasinlets 64 a-d. The key to controlling the wafer bias level is the RFpotential difference between the wafer pedestal 54 and the ceiling 52.Thus, either the pedestal RF power source 70 or the ceiling RF powersource 210 may be simply a short to RF ground. With such a programmableintegrated controller, the user can easily optimize apportionment of RFsource power, RF bias power and gas flow rate between the workpiececenter and periphery to achieve the greatest center-to-edge processuniformity across the surface of the workpiece (e.g., uniform radialdistribution of etch rate and etch selectivity). Also, by adjusting(through the controller 300) the RF power applied to the solenoids 42,90 relative to the RF power difference between the pedestal 54 andceiling 52, the user can operate the reactor in a predominantlyinductively coupled mode or in a predominantly capacitively coupledmode.

While the various power sources connected in FIG. 17A to the solenoids42, 90, the ceiling 52, side wall 50 (or the inner and outer ceilingportions 52 a, 52 b as in FIG. 17B) have been described as operating atRF frequencies, the invention is not restricted to any particular rangeof frequencies, and frequencies other than RF may be selected by theskilled worker in carrying out the invention.

In a preferred embodiment of the invention, the high thermalconductivity spacer 75, the ceiling 52 and the side wall 50 areintegrally formed together from a single piece of crystalline silicon.

While the invention has been described as being carried out with anumber of separate RF sources, some or all of the RF sources depictedherein may derive their outputs from separate RF generators or from acommon RF generator with different outputs at different RF power levels,frequencies and phases synthesized with variable power dividers,frequency multipliers and/or phase delays, as may be appropriate.Moreover, while the invention has been described as being carried outwith a number of separate process gas supplies, some or all of theprocess gas supplies may be derived from a common process gas supplywhich is divided among the plural separately controlled gas inlets 64.

While the invention has been described in detail by specific referenceto preferred embodiments, it is understood that variations andmodifications thereof may be made without departing from the true spiritand scope of the invention.

What is claimed is:
 1. A plasma chamber enclosure structure for use inan RF plasma reactor which includes a pedestal adapted to support aworkpiece to be processed, a reactor base housing the pedestal, and acoil antenna adjacent the reactor and which is adapted to inductivelycouple RF power into the reactor, said plasma chamber enclosurestructure comprising: a) said plasma chamber enclosure structure being asingle-wall dielectric enclosure structure; b) said plasma chamberenclosure structure being of an inverted cup-shape configuration; c)said plasma chamber enclosure structure having a substantially flat topcentral portion; d) said plasma chamber enclosure structure having aside wall portion generally transverse to said flat top central portion,said side wall portion having a height less than about half of adiameter of said flat top central portion, said plasma chamber enclosurestructure comprising a flange portion integrally formed with said sidewall portion, said flange portion being located distal from said flattop central portion and extending radially outward without extendinginward toward an interior of the chamber; e) said plasma chamberenclosure structure being adapted to cover the reactor base to comprisethe RF plasma reactor; f) said plasma chamber enclosure structure beingadapted to define a plasma processing volume over the pedestal; g) saidplasma chamber enclosure structure being capable of transmittinginductive power therethrough from an adjacent antenna; and h) saidplasma chamber enclosure structure being formed of a dielectric materialselected from the group consisting of silicon, silicon carbide, quartz,and alumina.
 2. The enclosure structure of claim 1 being adapted so asto be capable of having said flat top central portion in a facingrelationship to the pedestal when positioned over the base.
 3. Theenclosure structure of claim 2 being adapted to be positioned adjacentthe antenna.
 4. The enclosure structure of claim 3 wherein saiddielectric material consists of alumina.
 5. The enclosure structure ofclaim 1 having a generally right circular cylindrical configuration. 6.The enclosure structure of claim 1 wherein said dielectric materialconsists of alumina.
 7. The enclosure structure of claim 1 furthercomprising a conductive ceiling portion in a facing relationship to thepedestal when positioned over the base.
 8. The enclosure structure ofclaim 7 wherein said conductive ceiling portion is adapted to be coupledto a bias power source.
 9. A plasma chamber dome for an RF plasmareactor which includes a pedestal adapted to support a workpiece to beprocessed, a reactor base housing the pedestal, and a coil antennaadjacent the reactor and which is adapted to inductively couple RF powerinto the reactor, said dome comprising: a) said dome having an invertedcup-shape configuration having top and side walls in a generally rightcircular cylindrical configuration; b) said top wall comprising a flatcentral portion, said flat central portion having a diameter more thanabout twice a height of said side wall; c) said dome being adapted so asto be capable of having said flat central portion in a facingrelationship to the pedestal when positioned over the base; d) said domebeing adapted to define a plasma-processing volume over the pedestal,said dome comprising a flange integrally formed with said side wall,said flange being located distal from said top wall and extendingradially outward from said side wall without extending inward toward aninterior of the chamber; e) said dome being adapted to cover the reactorbase to comprise the RF plasma reactor; f) said dome being capable oftransmitting inductive power therethrough from an adjacent antenna; andg) said top wall and said side wall being formed of a dielectricmaterial selected from the group consisting of silicon, silicon carbide,quartz, alumina, and sapphire.
 10. The plasma chamber dome of claim 9wherein said top wall and said side wall consist of silicon.
 11. Theplasma chamber dome of claim 9 wherein said top wall and said side wallconsist of alumina.
 12. The plasma chamber dome of claim 9 comprising aconductive ceiling portion in a facing relationship to the pedestal whenpositioned over the base.
 13. The plasma chamber dome of claim 12wherein said conductive ceiling portion is adapted to be coupled to abias power source.
 14. An RF plasma reactor which includes a pedestaladapted to support a workpiece to be processed, a reactor base housingthe pedestal, and a coil antenna adjacent the reactor and which isadapted to inductively couple RF power into the reactor, the reactorcomprising: a) a single-wall dielectric enclosure structure of aninverted cup-shaped configuration having a substantially flat topcentral portion and a side wall portion, said side wall portion beinggenerally transverse to said flat top central portion, said side wallportion having a height less than about half of a diameter of said flattop central portion, said plasma chamber enclosure structure comprisinga flange portion integrally formed with said side wall portion, saidflange portion being located distal from said flat top central portionand extending radially outward without extending inward toward aninterior of the chamber; b) said single-wall dielectric enclosurestructure being adapted to cover the reactor base to comprise the RFplasma reactor; c) said single-wall dielectric enclosure structure beingadapted to define a plasma-processing volume over the pedestal; d) saidsingle-wall dielectric enclosure structure being capable of transmittinginductive power therethrough from an adjacent antenna; and e) saidsingle-wall dielectric enclosure structure being formed of a dielectricmaterial selected from the group consisting of silicon, silicon carbide,quartz, and alumina.
 15. The reactor of claim 14 wherein said topcentral flat portion when position over the base is in spaced facingrelationship to the pedestal.
 16. The reactor of claim 15 wherein saidenclosure structure consists of alumina.
 17. The reactor of claim 15wherein said side wall portion is adapted to be positioned adjacent theantenna.
 18. The reactor of claim 14 wherein said enclosure structurehas a generally right circular cylindrical configuration.
 19. Thereactor of claim 14 wherein said dielectric consists of alumina.
 20. Thereactor of claim 14 comprising a conductive ceiling portion in a facingrelationship to the pedestal when positioned over the base.
 21. Thereactor of claim 20 wherein said conductive ceiling portion is adaptedto be coupled to a bias power source.
 22. The enclosure structure ofclaim 1 being integrally formed of one of a) alumina, or b) silicon. 23.The plasma chamber dome of claim 9 being integrally formed of one of a)alumina, or b) silicon.
 24. The reactor of claim 14 wherein saidsingle-walled dielectric enclosure structure being integrally formed ofone of a) alumina, or b) silicon.